Modeling the effect of nitrogen input from feed on the nitrogen dynamics in an enclosed intensive culture pond of black tiger shrimp (Penaeus monodon)

In the present study, a mathematical model was developed to evaluate the effect of nitrogen (N) input from feed on the N dynamics under different feeding scenarios in a well aerated and enclosed culture pond of black tiger shrimp (Penaeus monodon). Three feeding levels were examined: underfeeding, optimum feeding and overfeeding. The model was formulated using field data gathered from an earthen pond (0.69 ha) which was stocked with shrimp post larvae at a density of 340,000 individuals ha(-1) and grown for 151 d. The model suggested that the underfeeding rate 329 kgNha(-1)cycle(-1)) observed from the study pond, which was being underfed, resulted in the ingestion of the natural productivity in the pond. With the underfeeding practice, phytoplankton assimilated ammonia and nitrate+nitrite at the rates of 412 and 52 kgNha(-1)cycle(-1), respectively, while nitrification rate in the water column was 45 kgNha(-1)cycle(-1). The coupled processes of nitrification and denitrification in sediment were nearly equal at rates averaging 207 and 206 kgNha(-1)cycle(-1), respectively. Optimum feeding indicated that the larger N input accelerated the accumulation of N in shrimp and phytoplankton as well as the accumulation of N in the water column and sediment. The coupled processes of nitrification and denitrification were accelerated to the rates of 298 and 292 kgNha(-1)cycle(-1). The overfeeding practice indicated that the extra N did not accelerate the process of N assimilation by phytoplankton due to light limitation, but accelerated the N processes in the sediment resulting in the active removal of N from the enclosed shrimp culture pond through the denitrification process (343 kgNha(-1)cycle(-1)). Thus, the mathematical model developed by the present study proved to be an effective tool in understanding N dynamics and gives informative data for farm management in the enclosed culture pond of black tiger shrimp.